The present invention relates to a tool device, comprising an exchange arm and a driving mechanism therefore, for a machining tool. Such machining tools exchange a tool on a spindle of a machine tool with a tool in a tool magazine.
Known machine tools can exchange a tool on a spindle with a tool in a tool magazine by a tool exchange arm. The body of the tool exchange arm is provided with sets of fingers which grip the tools on the spindle and in the tool magazine. By rotating the tool exchange arm, the fingers are rotated to exchange the tools.
Such tool exchange arm is proposed in Japanese Published Unexamined Application No. S63-123646, which uses a linkage. A rack is moved back and forth by rotating a pinion. A lever follows the movement of the rack to open and close gripping claws. Another tool exchange arm uses a hydraulic cylinder or the like to open and close the gripping claws.
These tool exchange arms have the following disadvantages. First, the tool exchange arms consist of a large number of components because of the linkage or hydraulic cylinder and thus are complex in structure. In addition, members connected directly or indirectly to the gripping claws are provided interlocking mechanisms or the like for controlling the fingers.
In the tool exchange arms using the linkage, the linkage has numerous pivots, and backlash tends to occur at the pivots. As a result, the movement of the fingers may not be correctly controlled, and the tool cannot be accurately gripped or set on the spindle or tool magazine.
In the structure described in Japanese Published Unexamined Patent Application No. S63-123646, the rack and the pinion compose an actuator for opening and closing the fingers. The actuator is driven to close the fingers for gripping the tool mounted on the spindle and the tool held in the tool magazine, respectively. Subsequently, the tool exchange arm is rotated about the axis of the body of the tool exchange arm, thereby exchanging the tool on the spindle with the tool in the tool magazine.
The tool exchange arm is rotated by rotating a hollow shaft mounted to the body of the tool exchange arm. A central shaft extends through the hollow shaft and rotates independently of the hollow shaft. The central shaft actuates the actuator for driving the fingers.
Since the tool exchange arm is provided with a drive mechanism including the hollow shaft and the central shaft, the size of the entire machine tool increases for the following two reasons: (1) a drive member for rotating the central shaft is installed outside the end of the central shaft at the opposite side of the tool exchange arm. The size of the central shaft increases in the direction of the central shaft, corresponding to the shape of the drive member; and (2) a member for supporting the hollow shaft is needed separately from a member for supporting the central shaft.